[codex] Use input items for Responses Lite tools (#27946)

When using Responses Lite, we should all use `additional_tools` and a
developer item instead of the top level tools array & instructions
field. This keeps things 1-to-1.

Forced namespacing for _all_ tools will land in a following PR after
some coordination & fixes in Responses API (around collisions & return
items).

The goal is to eventually expand the scope of this to _all_ requests
from codex, but that will require larger coordination across providers &
slower rollout.

codex-rs/codex-api/src/common.rs

@@ -28,7 +28,8 @@ pub struct CompactionInput<'a> {
     pub input: &'a [ResponseItem],
     #[serde(skip_serializing_if = "str::is_empty")]
     pub instructions: &'a str,
-    pub tools: Vec<Value>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub tools: Option<Vec<Value>>,
     pub parallel_tool_calls: bool,
     #[serde(skip_serializing_if = "Option::is_none")]
     pub reasoning: Option<Reasoning>,
@@ -210,7 +211,8 @@ pub struct ResponsesApiRequest {
     #[serde(skip_serializing_if = "String::is_empty")]
     pub instructions: String,
     pub input: Vec<ResponseItem>,
-    pub tools: Vec<serde_json::Value>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub tools: Option<Vec<serde_json::Value>>,
     pub tool_choice: String,
     pub parallel_tool_calls: bool,
     pub reasoning: Option<Reasoning>,
@@ -258,7 +260,8 @@ pub struct ResponseCreateWsRequest {
     #[serde(skip_serializing_if = "Option::is_none")]
     pub previous_response_id: Option<String>,
     pub input: Vec<ResponseItem>,
-    pub tools: Vec<Value>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub tools: Option<Vec<Value>>,
     pub tool_choice: String,
     pub parallel_tool_calls: bool,
     pub reasoning: Option<Reasoning>,

codex-rs/codex-api/src/endpoint/responses_websocket.rs

@@ -838,11 +838,11 @@ mod tests {
                 phase: None,
                 internal_chat_message_metadata_passthrough: None,
             }],
-            tools: vec![json!({
+            tools: Some(vec![json!({
                 "type": "function",
                 "name": "lookup",
                 "parameters": {"type": "object"}
-            })],
+            })]),
             tool_choice: "auto".to_string(),
             parallel_tool_calls: true,
             reasoning: None,

codex-rs/codex-api/tests/clients.rs

@@ -315,7 +315,7 @@ async fn responses_client_stream_request_preserves_item_ids() -> Result<()> {
             phase: None,
             internal_chat_message_metadata_passthrough: None,
         }],
-        tools: Vec::new(),
+        tools: Some(Vec::new()),
         tool_choice: "auto".into(),
         parallel_tool_calls: false,
         reasoning: None,
@@ -401,7 +401,7 @@ async fn streaming_client_retries_on_transport_error() -> Result<()> {
         model: "gpt-test".into(),
         instructions: "Say hi".into(),
         input: Vec::new(),
-        tools: Vec::new(),
+        tools: Some(Vec::new()),
         tool_choice: "auto".into(),
         parallel_tool_calls: false,
         reasoning: None,
@@ -520,7 +520,7 @@ async fn azure_store_sends_ids_and_headers() -> Result<()> {
             phase: None,
             internal_chat_message_metadata_passthrough: None,
         }],
-        tools: Vec::new(),
+        tools: Some(Vec::new()),
         tool_choice: "auto".into(),
         parallel_tool_calls: false,
         reasoning: None,

codex-rs/core/src/agent/control/spawn.rs

@@ -41,7 +41,8 @@ fn keep_forked_rollout_item(item: &RolloutItem, preserve_reference_context_item:
             _ => false,
         },
         RolloutItem::ResponseItem(
-            ResponseItem::AgentMessage { .. }
+            ResponseItem::AdditionalTools { .. }
+            | ResponseItem::AgentMessage { .. }
             | ResponseItem::Reasoning { .. }
             | ResponseItem::LocalShellCall { .. }
             | ResponseItem::FunctionCall { .. }

codex-rs/core/src/client.rs

@@ -73,6 +73,7 @@ use codex_otel::current_span_w3c_trace_context;
 use codex_protocol::ThreadId;
 use codex_protocol::config_types::ReasoningSummary as ReasoningSummaryConfig;
 use codex_protocol::config_types::Verbosity as VerbosityConfig;
+use codex_protocol::models::ContentItem;
 use codex_protocol::models::ResponseItem;
 use codex_protocol::openai_models::ModelInfo;
 use codex_protocol::openai_models::ReasoningEffort as ReasoningEffortConfig;
@@ -790,7 +791,6 @@ impl ModelClient {
         service_tier: Option<String>,
         responses_metadata: &CodexResponsesMetadata,
     ) -> Result<ResponsesApiRequest> {
-        let instructions = &prompt.base_instructions.text;
         let mut input = prompt.get_formatted_input_for_request(model_info.use_responses_lite);
         if !self.state.provider.info().is_openai() {
             input
@@ -798,6 +798,28 @@ impl ModelClient {
                 .for_each(ResponseItem::clear_internal_chat_message_metadata_passthrough);
         }
         let tools = create_tools_json_for_responses_api(&prompt.tools)?;
+        let (instructions, tools) = if model_info.use_responses_lite {
+            let mut prefix = vec![ResponseItem::AdditionalTools {
+                id: None,
+                role: "developer".to_string(),
+                tools,
+            }];
+            if !prompt.base_instructions.text.is_empty() {
+                prefix.push(ResponseItem::Message {
+                    id: None,
+                    role: "developer".to_string(),
+                    content: vec![ContentItem::InputText {
+                        text: prompt.base_instructions.text.clone(),
+                    }],
+                    phase: None,
+                    internal_chat_message_metadata_passthrough: None,
+                });
+            }
+            input.splice(0..0, prefix);
+            (String::new(), None)
+        } else {
+            (prompt.base_instructions.text.clone(), Some(tools))
+        };
         let reasoning = Self::build_reasoning(model_info, effort, summary);
         let include = if reasoning.is_some() {
             vec!["reasoning.encrypted_content".to_string()]
@@ -824,7 +846,7 @@ impl ModelClient {
         let service_tier = model_info.service_tier_for_request(service_tier);
         let request = ResponsesApiRequest {
             model: model_info.slug.clone(),
-            instructions: instructions.clone(),
+            instructions,
             input,
             tools,
             tool_choice: "auto".to_string(),

codex-rs/core/src/client_common.rs

@@ -83,7 +83,8 @@ fn strip_image_details(items: &mut [ResponseItem]) {
                     }
                 }
             }
-            ResponseItem::Reasoning { .. }
+            ResponseItem::AdditionalTools { .. }
+            | ResponseItem::Reasoning { .. }
             | ResponseItem::AgentMessage { .. }
             | ResponseItem::LocalShellCall { .. }
             | ResponseItem::FunctionCall { .. }

codex-rs/core/src/client_common_tests.rs

@@ -110,7 +110,7 @@ fn serializes_text_verbosity_when_set() {
         model: "gpt-5.4".to_string(),
         instructions: "i".to_string(),
         input,
-        tools,
+        tools: Some(tools),
         tool_choice: "auto".to_string(),
         parallel_tool_calls: true,
         reasoning: None,
@@ -157,7 +157,7 @@ fn serializes_text_schema_with_strict_format() {
         model: "gpt-5.4".to_string(),
         instructions: "i".to_string(),
         input,
-        tools,
+        tools: Some(tools),
         tool_choice: "auto".to_string(),
         parallel_tool_calls: true,
         reasoning: None,
@@ -218,7 +218,7 @@ fn omits_text_when_not_set() {
         model: "gpt-5.4".to_string(),
         instructions: "i".to_string(),
         input,
-        tools,
+        tools: Some(tools),
         tool_choice: "auto".to_string(),
         parallel_tool_calls: true,
         reasoning: None,
@@ -241,7 +241,7 @@ fn serializes_flex_service_tier_when_set() {
         model: "gpt-5.4".to_string(),
         instructions: "i".to_string(),
         input: vec![],
-        tools: vec![],
+        tools: Some(vec![]),
         tool_choice: "auto".to_string(),
         parallel_tool_calls: true,
         reasoning: None,

codex-rs/core/src/compact_remote.rs

@@ -352,7 +352,8 @@ pub(crate) fn should_keep_compacted_history_item(item: &ResponseItem) -> bool {
         ResponseItem::AgentMessage { .. } => true,
         ResponseItem::Compaction { .. } | ResponseItem::ContextCompaction { .. } => true,
         ResponseItem::CompactionTrigger { .. } => false,
-        ResponseItem::Reasoning { .. }
+        ResponseItem::AdditionalTools { .. }
+        | ResponseItem::Reasoning { .. }
         | ResponseItem::LocalShellCall { .. }
         | ResponseItem::FunctionCall { .. }
         | ResponseItem::ToolSearchCall { .. }

codex-rs/core/src/context_manager/history.rs

@@ -386,7 +386,8 @@ impl ContextManager {
                 output: truncate_function_output_payload(output, policy_with_serialization_budget),
                 internal_chat_message_metadata_passthrough: metadata.clone(),
             },
-            ResponseItem::Message { .. }
+            ResponseItem::AdditionalTools { .. }
+            | ResponseItem::Message { .. }
             | ResponseItem::AgentMessage { .. }
             | ResponseItem::Reasoning { .. }
             | ResponseItem::LocalShellCall { .. }
@@ -476,7 +477,8 @@ pub(crate) fn truncate_function_output_payload(
 fn is_api_message(message: &ResponseItem) -> bool {
     match message {
         ResponseItem::Message { role, .. } => role.as_str() != "system",
-        ResponseItem::AgentMessage { .. }
+        ResponseItem::AdditionalTools { .. }
+        | ResponseItem::AgentMessage { .. }
         | ResponseItem::FunctionCallOutput { .. }
         | ResponseItem::FunctionCall { .. }
         | ResponseItem::ToolSearchCall { .. }
@@ -722,7 +724,8 @@ fn is_model_generated_item(item: &ResponseItem) -> bool {
         | ResponseItem::Compaction { .. }
         | ResponseItem::ContextCompaction { .. } => true,
         ResponseItem::CompactionTrigger { .. } => false,
-        ResponseItem::FunctionCallOutput { .. }
+        ResponseItem::AdditionalTools { .. }
+        | ResponseItem::FunctionCallOutput { .. }
         | ResponseItem::ToolSearchOutput { .. }
         | ResponseItem::CustomToolCallOutput { .. }
         | ResponseItem::AgentMessage { .. }

codex-rs/core/src/image_preparation.rs

@@ -57,7 +57,8 @@ pub(crate) fn prepare_response_items(items: &mut [ResponseItem]) {
                     prepare_tool_output_content(content);
                 }
             }
-            ResponseItem::Reasoning { .. }
+            ResponseItem::AdditionalTools { .. }
+            | ResponseItem::Reasoning { .. }
             | ResponseItem::AgentMessage { .. }
             | ResponseItem::LocalShellCall { .. }
             | ResponseItem::FunctionCall { .. }

codex-rs/core/src/session/mod.rs

@@ -2715,6 +2715,7 @@ impl Session {
                 continue;
             }
             let prefix = match item {
+                ResponseItem::AdditionalTools { .. } => "at",
                 ResponseItem::Message { .. } => "msg",
                 ResponseItem::Reasoning { .. } => "rs",
                 ResponseItem::LocalShellCall { .. } => "lsh",

codex-rs/core/src/session/tests.rs

@@ -222,6 +222,19 @@ fn assign_missing_response_item_ids_skips_agent_messages() {
     assert!(items[1].id().is_some_and(|id| id.starts_with("msg_")));
 }
 
+#[test]
+fn assign_missing_response_item_ids_assigns_additional_tools_ids() {
+    let items = Cow::Owned(vec![ResponseItem::AdditionalTools {
+        id: None,
+        role: "developer".to_string(),
+        tools: Vec::new(),
+    }]);
+
+    let items = Session::assign_missing_response_item_ids(items);
+
+    assert!(items[0].id().is_some_and(|id| id.starts_with("at_")));
+}
+
 fn assistant_message(text: &str) -> ResponseItem {
     ResponseItem::Message {
         id: None,

codex-rs/core/src/session/turn.rs

@@ -2091,7 +2091,8 @@ async fn try_run_sampling_request(
                     }
                     ResponseItem::Reasoning { .. } => true,
                     ResponseItem::AgentMessage { .. } => false,
-                    ResponseItem::LocalShellCall { .. }
+                    ResponseItem::AdditionalTools { .. }
+                    | ResponseItem::LocalShellCall { .. }
                     | ResponseItem::FunctionCall { .. }
                     | ResponseItem::ToolSearchCall { .. }
                     | ResponseItem::FunctionCallOutput { .. }

codex-rs/core/src/turn_timing.rs

@@ -380,7 +380,8 @@ fn response_item_records_turn_ttft(item: &ResponseItem) -> bool {
         | ResponseItem::Compaction { .. }
         | ResponseItem::ContextCompaction { .. } => true,
         ResponseItem::CompactionTrigger { .. } => false,
-        ResponseItem::FunctionCallOutput { .. }
+        ResponseItem::AdditionalTools { .. }
+        | ResponseItem::FunctionCallOutput { .. }
         | ResponseItem::CustomToolCallOutput { .. }
         | ResponseItem::ToolSearchOutput { .. }
         | ResponseItem::Other => false,

codex-rs/core/tests/suite/agent_websocket.rs

@@ -1,6 +1,10 @@
 use anyhow::Result;
 use codex_features::Feature;
 use codex_protocol::config_types::ServiceTier;
+use codex_protocol::protocol::EventMsg;
+use codex_protocol::protocol::Op;
+use codex_protocol::protocol::ThreadSettingsOverrides;
+use codex_protocol::user_input::UserInput;
 use core_test_support::responses::WebSocketConnectionConfig;
 use core_test_support::responses::ev_assistant_message;
 use core_test_support::responses::ev_completed;
@@ -10,12 +14,89 @@ use core_test_support::responses::start_websocket_server;
 use core_test_support::responses::start_websocket_server_with_headers;
 use core_test_support::skip_if_no_network;
 use core_test_support::test_codex::test_codex;
+use core_test_support::wait_for_event;
 use pretty_assertions::assert_eq;
 use serde_json::Value;
 use std::time::Duration;
 
 const WS_V2_BETA_HEADER_VALUE: &str = "responses_websockets=2026-02-06";
 
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn websocket_model_switch_to_responses_lite_omits_top_level_tools() -> Result<()> {
+    skip_if_no_network!(Ok(()));
+
+    let server = start_websocket_server(vec![vec![
+        vec![ev_response_created("warm-1"), ev_completed("warm-1")],
+        vec![ev_response_created("resp-1"), ev_completed("resp-1")],
+        vec![ev_response_created("resp-2"), ev_completed("resp-2")],
+    ]])
+    .await;
+
+    let mut builder = test_codex()
+        .with_model_info_override("gpt-5.4", |model_info| {
+            model_info.use_responses_lite = true;
+        })
+        .with_model("gpt-5.3-codex");
+    let test = builder.build_with_websocket_server(&server).await?;
+
+    test.submit_turn("non-lite turn").await?;
+    test.codex
+        .submit(Op::UserInput {
+            items: vec![UserInput::Text {
+                text: "lite turn".into(),
+                text_elements: Vec::new(),
+            }],
+            final_output_json_schema: None,
+            responsesapi_client_metadata: None,
+            additional_context: Default::default(),
+            thread_settings: ThreadSettingsOverrides {
+                model: Some("gpt-5.4".to_string()),
+                ..Default::default()
+            },
+        })
+        .await?;
+    wait_for_event(&test.codex, |event| {
+        matches!(event, EventMsg::TurnComplete(_))
+    })
+    .await;
+
+    assert_eq!(server.handshakes().len(), 1);
+    let connection = server.single_connection();
+    assert_eq!(connection.len(), 3);
+    let non_lite_turn = connection
+        .get(1)
+        .expect("missing non-lite turn request")
+        .body_json();
+    let lite_turn = connection
+        .get(2)
+        .expect("missing lite turn request")
+        .body_json();
+
+    assert_eq!(non_lite_turn["model"].as_str(), Some("gpt-5.3-codex"));
+    assert_eq!(lite_turn["model"].as_str(), Some("gpt-5.4"));
+    assert!(
+        non_lite_turn
+            .get("tools")
+            .and_then(Value::as_array)
+            .is_some_and(|tools| !tools.is_empty())
+    );
+    assert_eq!(lite_turn.get("previous_response_id"), None);
+    assert_eq!(lite_turn.get("tools"), None);
+    assert_eq!(lite_turn.get("instructions"), None);
+    let additional_tools = lite_turn
+        .get("input")
+        .and_then(Value::as_array)
+        .and_then(|input| input.first())
+        .filter(|item| item.get("type").and_then(Value::as_str) == Some("additional_tools"))
+        .and_then(|item| item.get("tools"))
+        .and_then(Value::as_array)
+        .expect("lite turn should start with an additional_tools item");
+    assert!(!additional_tools.is_empty());
+
+    server.shutdown().await;
+    Ok(())
+}
+
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
 async fn websocket_test_codex_shell_chain() -> Result<()> {
     skip_if_no_network!(Ok(()));

codex-rs/core/tests/suite/responses_lite.rs

@@ -54,6 +54,70 @@ fn has_hosted_tool(tools: &[Value], tool_type: &str) -> bool {
         .any(|tool| tool.get("type").and_then(Value::as_str) == Some(tool_type))
 }
 
+fn additional_tools(body: &Value) -> Result<&[Value]> {
+    body["input"]
+        .as_array()
+        .context("Responses request input should be an array")?
+        .first()
+        .filter(|item| item.get("type").and_then(Value::as_str) == Some("additional_tools"))
+        .context("Responses request should start with additional_tools")?["tools"]
+        .as_array()
+        .map(Vec::as_slice)
+        .context("additional_tools tools should be an array")
+}
+
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn responses_lite_uses_input_items_for_instructions_and_tools() -> Result<()> {
+    skip_if_no_network!(Ok(()));
+
+    let server = responses::start_mock_server().await;
+    let response_mock = responses::mount_sse_once(
+        &server,
+        responses::sse(vec![
+            responses::ev_response_created("resp-1"),
+            responses::ev_completed("resp-1"),
+        ]),
+    )
+    .await;
+
+    let mut builder = test_codex()
+        .with_model_info_override("gpt-5.4", |model_info| {
+            model_info.use_responses_lite = true;
+        })
+        .with_config(|config| {
+            config.base_instructions = Some("test instructions".to_string());
+        });
+    let test = builder.build(&server).await?;
+
+    test.submit_turn("hello").await?;
+
+    let body = response_mock.single_request().body_json();
+    assert!(body.get("instructions").is_none());
+    assert!(body.get("tools").is_none());
+
+    let input = body["input"]
+        .as_array()
+        .context("Responses request input should be an array")?;
+    assert_eq!(input[0]["type"], "additional_tools");
+    assert_eq!(input[0]["role"], "developer");
+    assert_eq!(
+        input[1],
+        serde_json::json!({
+            "type": "message",
+            "role": "developer",
+            "content": [{
+                "type": "input_text",
+                "text": "test instructions",
+            }],
+        })
+    );
+
+    let tools = additional_tools(&body)?;
+    assert!(!tools.is_empty());
+
+    Ok(())
+}
+
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
 async fn responses_lite_prepares_images() -> Result<()> {
     skip_if_no_network!(Ok(()));
@@ -158,17 +222,10 @@ async fn responses_lite_uses_standalone_web_search_and_image_generation() -> Res
         request.header(RESPONSES_LITE_HEADER).as_deref(),
         Some("true")
     );
-    request
-        .tool_by_name("web", "run")
-        .context("Responses Lite should expose standalone web search")?;
-    request
-        .tool_by_name("image_gen", "imagegen")
-        .context("Responses Lite should expose standalone image generation")?;
-
     let body = request.body_json();
-    let tools = body["tools"]
+    assert!(body.get("tools").is_none());
-        .as_array()
+    let tools = additional_tools(&body)?;
-        .context("Responses request tools should be an array")?;
+    assert!(!tools.is_empty());
     assert!(!has_hosted_tool(tools, "web_search"));
     assert!(!has_hosted_tool(tools, "image_generation"));
 
@@ -256,9 +313,8 @@ async fn responses_lite_omits_hosted_tools_without_standalone_extensions() -> Re
     test.submit_turn("Do not use hosted tools").await?;
 
     let body = response_mock.single_request().body_json();
-    let tools = body["tools"]
+    assert!(body.get("tools").is_none());
-        .as_array()
+    let tools = additional_tools(&body)?;
-        .context("Responses request tools should be an array")?;
     assert!(!has_hosted_tool(tools, "web_search"));
     assert!(!has_hosted_tool(tools, "image_generation"));
 

codex-rs/ext/image-generation/src/tool.rs

@@ -256,7 +256,8 @@ fn recent_images(history: &[ResponseItem], count: usize) -> Vec<ImageUrl> {
             ResponseItem::CustomToolCall { call_id, .. } => {
                 custom_tool_call_ids.insert(call_id.as_str());
             }
-            ResponseItem::Message { .. }
+            ResponseItem::AdditionalTools { .. }
+            | ResponseItem::Message { .. }
             | ResponseItem::AgentMessage { .. }
             | ResponseItem::Reasoning { .. }
             | ResponseItem::LocalShellCall { .. }
@@ -296,7 +297,8 @@ fn recent_images(history: &[ResponseItem], count: usize) -> Vec<ImageUrl> {
             ResponseItem::ImageGenerationCall { result, .. } if !result.is_empty() => {
                 image_urls.push(format!("data:image/png;base64,{result}"));
             }
-            ResponseItem::Reasoning { .. }
+            ResponseItem::AdditionalTools { .. }
+            | ResponseItem::Reasoning { .. }
             | ResponseItem::AgentMessage { .. }
             | ResponseItem::LocalShellCall { .. }
             | ResponseItem::FunctionCall { .. }

codex-rs/otel/src/events/session_telemetry.rs

@@ -1198,6 +1198,7 @@ impl SessionTelemetry {
 
     fn responses_item_type(item: &ResponseItem) -> String {
         match item {
+            ResponseItem::AdditionalTools { .. } => "additional_tools".into(),
             ResponseItem::Message { role, .. } => format!("message_from_{role}"),
             ResponseItem::AgentMessage { .. } => "agent_message".into(),
             ResponseItem::Reasoning { .. } => "reasoning".into(),

codex-rs/protocol/src/models.rs

@@ -932,6 +932,14 @@ impl InternalChatMessageMetadataPassthrough {
 #[derive(Debug, Clone, Serialize, Deserialize, PartialEq, JsonSchema, TS)]
 #[serde(tag = "type", rename_all = "snake_case")]
 pub enum ResponseItem {
+    #[schemars(skip)]
+    #[ts(skip)]
+    AdditionalTools {
+        #[serde(default, skip_serializing_if = "Option::is_none")]
+        id: Option<String>,
+        role: String,
+        tools: Vec<serde_json::Value>,
+    },
     Message {
         #[serde(default, skip_serializing_if = "Option::is_none")]
         #[ts(optional)]
@@ -1160,7 +1168,8 @@ impl ResponseItem {
     /// Returns the non-empty Responses API item ID, if present.
     pub fn id(&self) -> Option<&str> {
         match self {
-            Self::Message { id, .. }
+            Self::AdditionalTools { id, .. }
+            | Self::Message { id, .. }
             | Self::AgentMessage { id, .. }
             | Self::LocalShellCall { id, .. }
             | Self::FunctionCall { id, .. }
@@ -1181,7 +1190,8 @@ impl ResponseItem {
     /// Sets or clears the Responses API item ID for variants that carry one.
     pub fn set_id(&mut self, new_id: Option<String>) {
         match self {
-            Self::Message { id, .. }
+            Self::AdditionalTools { id, .. }
+            | Self::Message { id, .. }
             | Self::AgentMessage { id, .. }
             | Self::LocalShellCall { id, .. }
             | Self::FunctionCall { id, .. }
@@ -1282,7 +1292,7 @@ impl ResponseItem {
                 internal_chat_message_metadata_passthrough: metadata,
                 ..
             } => metadata.as_ref(),
-            Self::CompactionTrigger { .. } | Self::Other => None,
+            Self::CompactionTrigger { .. } | Self::AdditionalTools { .. } | Self::Other => None,
         }
     }
 
@@ -1346,7 +1356,7 @@ impl ResponseItem {
                 internal_chat_message_metadata_passthrough: metadata,
                 ..
             } => Some(metadata),
-            Self::CompactionTrigger { .. } | Self::Other => None,
+            Self::CompactionTrigger { .. } | Self::AdditionalTools { .. } | Self::Other => None,
         }
     }
 }
@@ -2237,6 +2247,14 @@ mod tests {
         item.set_id(/*new_id*/ None);
 
         assert_eq!(item.id(), None);
+
+        let mut additional_tools = ResponseItem::AdditionalTools {
+            id: None,
+            role: "developer".to_string(),
+            tools: Vec::new(),
+        };
+        additional_tools.set_id(Some("at_test".to_string()));
+        assert_eq!(additional_tools.id(), Some("at_test"));
     }
 
     fn response_item_with_passthrough_metadata(

codex-rs/rollout-trace/src/reducer/conversation/normalize.rs

@@ -37,6 +37,9 @@ pub(super) fn normalize_model_items(
 ) -> Result<Vec<NormalizedConversationItem>> {
     let mut normalized_items = Vec::new();
     for item in items {
+        if item.get("type").and_then(Value::as_str) == Some("additional_tools") {
+            continue;
+        }
         normalized_items.push(normalize_model_item(item, raw_payload)?);
     }
     Ok(normalized_items)

codex-rs/rollout-trace/src/reducer/conversation_tests.rs

@@ -735,6 +735,48 @@ fn unsupported_model_item_is_reducer_error() -> anyhow::Result<()> {
     )
 }
 
+#[test]
+fn additional_tools_are_excluded_from_request_conversation() -> anyhow::Result<()> {
+    let temp = TempDir::new()?;
+    let writer = create_started_writer(&temp)?;
+    start_turn(&writer, "turn-1")?;
+
+    let request = writer.write_json_payload(
+        RawPayloadKind::InferenceRequest,
+        &json!({
+            "input": [
+                {
+                    "type": "additional_tools",
+                    "role": "developer",
+                    "tools": [{
+                        "type": "function",
+                        "name": "lookup",
+                        "parameters": {"type": "object", "properties": {}}
+                    }]
+                },
+                message("user", "find it")
+            ]
+        }),
+    )?;
+    append_inference_start(&writer, "inference-1", "turn-1", request)?;
+
+    let rollout = replay_bundle(temp.path())?;
+    let request_item_ids = &rollout.inference_calls["inference-1"].request_item_ids;
+
+    assert_eq!(request_item_ids.len(), 1);
+    assert_eq!(rollout.conversation_items.len(), 1);
+    assert_eq!(
+        rollout.conversation_items[&request_item_ids[0]].body,
+        ConversationBody {
+            parts: vec![ConversationPart::Text {
+                text: "find it".to_string(),
+            }],
+        }
+    );
+
+    Ok(())
+}
+
 #[test]
 fn missing_request_input_is_reducer_error() -> anyhow::Result<()> {
     let temp = TempDir::new()?;

codex-rs/rollout/src/policy.rs

@@ -44,8 +44,9 @@ pub fn should_persist_response_item(item: &ResponseItem) -> bool {
         | ResponseItem::ImageGenerationCall { .. }
         | ResponseItem::Compaction { .. }
         | ResponseItem::ContextCompaction { .. } => true,
-        ResponseItem::CompactionTrigger { .. } => false,
+        ResponseItem::AdditionalTools { .. }
-        ResponseItem::Other => false,
+        | ResponseItem::CompactionTrigger { .. }
+        | ResponseItem::Other => false,
     }
 }
 
@@ -62,7 +63,8 @@ pub fn should_persist_response_item_for_memories(item: &ResponseItem) -> bool {
         | ResponseItem::CustomToolCall { .. }
         | ResponseItem::CustomToolCallOutput { .. }
         | ResponseItem::WebSearchCall { .. } => true,
-        ResponseItem::AgentMessage { .. }
+        ResponseItem::AdditionalTools { .. }
+        | ResponseItem::AgentMessage { .. }
         | ResponseItem::Reasoning { .. }
         | ResponseItem::ImageGenerationCall { .. }
         | ResponseItem::Compaction { .. }